As is well known in the gas turbine engine technology, there is a continual effort to maintain the concentricity of the stationary and rotating parts of the engine and to assure that the high temperature and the hostile environment to which an engine is subjected, does not adversely affect this concentricity. For example, U.S. Pat. No. 5,118,253 granted to James T. Balkcum, III on Jun. 2, 1992 entitled "COMPRESSOR CASE CONSTRUCTION WITH BACKBONE", U.S. Pat. No. 5,180,281 granted to Joseph C. Burge, et al on Jan. 19, 1993 entitled "CASE TYING MEANS FOR GAS TURBINE ENGINE", and U.S. Pat. No. 5,127,797 granted to Kenneth E. Carman on Jul. 7, 1992 entitled "COMPRESSOR CASE ATTACHMENT MEANS" which are commonly assigned to the same assignee as the present patent application, disclose means for attaching the stator and its vanes of the compressor to the engine case. The U.S. Pat. Nos. 5,118,253 and 5,127,797, supra, in particular, include means for permitting circumferential thermal growth and axial and circumferential thermal growth, while restraining radial movement.
As noted in the aforementioned patents, the engine case is relatively thin compared to the rotor and stator components in the compressor section. Hence, the case responds more rapidly to temperature changes than do these other components. Obviously, it is important to hold the clearances of the rotating components and the stationary components surrounding the rotor (outer air seal), in order to assure optimum engine operating performance. Because these clearances are so minute, it inherently is a difficult problem to maintain concentricity of the stator to assure that the tips of the turbine blades in an axial flow turbine do not rub against the outer air seal during the transient conditions where extreme changes in the temperature and mechanical loads are encountered.
The U.S. Pat. No. 5,118,253, supra, attempts to resolve this problem by providing a tongue and groove attachment to the backbone and utilizing a single bolt located intermediate the ends of the stator that extends from the stator to the outer case. Obviously, this mechanical arrangement provides a rigid connection with the ends being sufficiently flexible to allow for the circumferential thermal growth.
The U.S. Pat. No. 5,127,797, supra, includes a tongue and groove assembly that is bolted to the outer case for supporting the stator to the case. This tying assembly, like the structure disclosed in U.S. Pat. No. 5,118,253, supra, forms a rigid connection to the case and stator.
The U.S. Pat. No. 5,180,281, supra, includes a segmented rail with bosses that are adapted to receive bolts for attaching the stator to the case. The portion of the segmented rail between the bosses is made relatively thin so as to be flexible that serves to accommodate the changes in the thermals. Again, this tying arrangement is a rigid connection between the case and stator.
While these rigid types of structures for tying the stator vanes to the outer case are efficacious for certain applications, they are not completely satisfactory for other applications.
Also worthy of note are U.S. Pat. No. 4,920,742 granted to Mash et al on May 1, 1990 and entitled "HEAT SHIELD FOR GAS TURBINE ENGINE FRAME", and U.S. Pat. No. 4,987,736 granted to Ciokajlo et al on Jan. 29, 1991 and entitled "LIGHTWEIGHT GAS TURBINE ENGINE FRAME WITH FREE-FLOATING HEAT SHIELD", respectively. The U.S. Pat. No. 4,920,742, supra, is a liner for protecting the frame of the engine from extreme temperatures and discloses a support assembly for allowing the frame to float freely to avoid the thermal stresses that would otherwise cause warping and malfunctioning of this component. It is noted that the expansion and contraction is in the axial, circumferential and radial directions.
The U.S. Pat. No. 4,987,736, supra, likewise is directed to the heat shield for the turbine discharge gases and relies on nut and bolt assemblies for free floating the heat shield. Likewise, the direction of contraction and expansion is similar to the direction disclosed in the U.S. Pat. No. 4,920,742.
In contrast, this invention particularly addresses problems in the compressor case and relies on a judicious selection of the lug nuts, pins, and bolt assemblies and the discrete tolerances of certain components for allowing the expansion and contraction for thermals in the axial and circumferential directions while restraining movement of the components in the radial direction. In particular, the lug nuts relative to the hook assembly for the stator vanes are free to move and hence, are "floating". This invention contemplates joining three rows of stator vanes to form an integral arcuate segment and joining nine such segments to form an annular stator vane configuration. Three lugs or lug nuts supported in hooks extending radially from the outer diameter of the stator case or shroud are tied to the engine's outer case by a machine bolt and operatively connected to the hooks by pins. The three lugs and hook assemblies for each stator segment are circumferentially spaced in each stator segment and the pins at the end lugs are loosely supported in the hooks and the pins in the center lug are tightly supported in the circumferential direction of the hooks and loosely disposed in the axial direction. The center pin is thusly dimensioned so that it can grow axially while being restrained circumferentially and radially. The overall arrangement of these pins and their relationship to the respective slots allow for the constraints noted immediately above while the ends are capable of expanding and contracting in the axial and circumferential directions. Discrete tolerances between adjacent integral stators allow for axial growth and avoid binding as a result of the thermals.